The invention relates to a pump having a cutting wheel and a pre-cutter for cutting chippings that are contained in the medium pumped by the pump, the pre-cutter being driven by a shaft portion that projects axially from the cutting wheel and having a plurality of wings, the pre-cutter being surrounded by a crest of anvil blocks at which the free ends of the wings move past in a little distance when the pre-cutter rotates.
A pump of this type is known from DE 10 2008 031 842 B3 and is used for example in machine tools for circulating lubricating coolant emulsions that are contaminated with metal chippings. This pump is a centrifugal pump that has, in addition to a radial impeller, an axial impeller disposed upstream of the radial impeller, said axial impeller being configured as a cutting impeller and having, at its upstream end, cutting edges that cooperate with stationary counter blades arranged radially in a suction passage, so that chippings and other contaminants that have been sucked in are cut-off and chopped. The pre-cutter serves for chopping coarse contaminants before they are sucked-in by the axial impeller and are then chopped further. In this pump, the anvil blocks are formed by the intake port of the pump having, at the level of the pre-cutter, a non-circular, approximately polygonal cross-section.